diff --git a/ext/dl/handle.c b/ext/dl/handle.c
index 9ca2fa0a54..95b6dc74dc 100644
--- a/ext/dl/handle.c
+++ b/ext/dl/handle.c
@@ -52,11 +52,11 @@ rb_dlhandle_initialize(int argc, VALUE argv[], VALUE self)
 
   switch (rb_scan_args(argc, argv, "11", &lib, &flag)) {
   case 1:
-    clib = StringValuePtr(lib);
+    clib = NIL_P(lib) ? NULL : StringValuePtr(lib);
     cflag = RTLD_LAZY | RTLD_GLOBAL;
     break;
   case 2:
-    clib = StringValuePtr(lib);
+    clib = NIL_P(lib) ? NULL : StringValuePtr(lib);
     cflag = NUM2INT(flag);
     break;
   default: